Ratcheting one-way clutch having rockers actuated by centrifugal force

ABSTRACT

A ratcheting one-way clutch includes a cam plate formed with cam surfaces angularly spaced about a central axis, and a rocker plate having pockets angularly spaced about the central axis, each pocket including a surface having a pivot axis located within the pocket. A rocker, located in each pocket, pivots about the pivot axis toward and away from the cam surfaces. Each rocker has a center of mass, located relative to the pivot axis when the rocker is retracted into the pocket away from the cam surfaces, such that an acute angle formed between a first line that extends radially from the central axis through the pivot axis and a second line that passes through the center of mass and the pivot axis is equal to or less than twenty degrees.

CROSS REFERENCE TO RELATED APPLICATION

This application is a continuation-in-part of pending U.S. applicationSer. No. 10/899,918, filed Jul. 27, 2004.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates in general to a clutch that produces a driveconnection between components when their relative rotation is in onedirection, and overruns when relative rotation is in the oppositedirection. In particular, the invention pertains to such clutches havingrockers that engage or disengage at least partially due to the effect ofcentrifugal force acting on the rocker.

2. Description of the Prior Art

Conventional one-way clutches for producing a one-way drive connectionbetween inner and outer races of the clutch include sprags or rollersfor releasably driveably connecting the races and the components of amechanical assembly connected to the races. Such clutches are commonlyused in the powertrain or driveline of an automotive vehicle. One-wayclutches perform satisfactorily in many cases, but certain applications,such as those in which large magnitudes of torque are transmitted by theclutch, or those that provide only a small space for the clutch, requireone-way clutches other than conventional sprag-type or roller-typeclutch to meet desire requirements.

Conventional one-way clutch assemblies have at least one sprag orroller, which driveably locks two notched or pocketed races togethermutually in one rotary direction and allows the races to rotate freelyin the other direction. Rocker and sprag type one-way clutch assembliescan increase the torque capacity for a given package size compared tothose of a roller-type clutch, but they are generally limited in torquetransmitting capacity by the magnitude of the contact or bearingstresses caused by contact of the rockers or sprags with the races.

To overcome these and other difficulties, a one-way overrunning clutchdescribed in U.S. Pat. No. 5,070,978 includes a drive member and adriven member, which are mounted for clockwise and counterclockwiserotation about a common axis. The drive member includes a planar driveface, normal to the common axis, which connects with a source of powerfor rotating the planar drive face either clockwise or counterclockwise.The driven member includes a planar driven face, positioned in closeproximity to and in confronting relationship with the drive face. Thedrive and driven members are coupled to one another through a series ofpockets in one of the drive faces, and a plurality of cooperating strutscarried by the other face, such that when the drive member is drivencounterclockwise, it drives the driven member with it. When the drivemember is driven clockwise, it does not drive the driven member, butrotates freely relative to the driven member. Column stability of thestrut, which transmits the torsion load between the races, is animportance factor in the design.

U.S. Pat. No. 5,954,174 discloses a ratchet one-way clutch assemblyhaving an inner race with notches, an outer race with pockets, androckers located in the pockets to engage the notches. The rockers have apivot ridge which mates with a peak or recess in the pockets in theouter race to position the rocker in the pocket. The center of mass ofeach rocker is located such that the rocker tends to engage or disengagea notch in the inner race. A spring is used to provide a tilting forceon each rocker directed to produce engagement of the rocker with anotch.

Conventional one-way clutches develop relatively large magnitudes ofhoop stress in the races when torque is transmitted through the clutch;therefore, the races of conventional one-way clutches are formed ofbearing grade steel in order to withstand the operating hoop stress.Because the clutches disclosed in the '978 and '245 patents developrelative low operating hoop stresses in service, those clutch can beformed of powered metal. Clutches formed for powered metal potentiallycan be produced at relative low cost compared to the cost to form andproduce a conventional clutch of high grade steel, provided extensivemachining is avoided.

The clutches described in the '978 or '245 patents, however, require asignificant amount of machining of the components that are formed ofpowered metal. Excessive internal backlash, which can produce noise atunacceptable levels, is a potentially problem under certain operatingconditions with these clutches.

A need exits, therefore, for a low cost, reliable one-way clutch thatproduces low operating bearing stresses and is able to be formed readilyfrom powered metal. The clutch should occupy little space, minimizein-service noise, and require little or no machining. Preferably, thedesired clutch should include features that facilitate its assembly in adrive system.

SUMMARY OF THE INVENTION

The present invention provides a one-way clutch having an inner race,outer race, and pivoting rockers that driveably connect the races in onerotary direction and overrun in the opposite direction. The clutch ispreferably formed of powered metal.

The rockers are located in one of the races, such that the clutch canemploy centrifugal force to assist in disengaging the rockers from a camplate during an overrun condition by biasing the rockers to pivot awayfrom the cam plate. Alternately, the clutch can employ centrifugal forceto assist in engaging the rockers with the cam notch plate by urging therockers to pivot toward the cam plate.

The shape of a pocket plate, which contains the rockers, uniquelyrequires no secondary machining operations for any purpose, such as toeliminate densifiers and de-densifiers in the powered metal components.The components of the clutch that are formed from powered metal requireno machining after they are formed.

The number of notches for a given diameter is greater than other one-wayclutches, thereby significantly reducing backlash. The design lendsitself to easy assembly due to its configuration. A rocker platesubassembly contains the rockers and, preferably, a return spring foreach rocker. Before its assembly in the clutch, the rocker platesubassembly restricts the ability of each rocker to pivot in the pocket,and the force of the respective return spring prevents the rocker fromexiting the pocket laterally by forcing the rocker into contact with itspocket. This arrangement permits that subassembly to be handled andtransported prior to its installation in the clutch with the rockers andsprings already installed in the pocket plate subassembly.

A ratcheting one-way clutch, according to this invention, includes a camplate formed with cam surfaces angularly spaced about a central axis,and a rocker plate having pockets angularly spaced about the centralaxis, each pocket including a surface having a pivot axis located withinthe pocket. A rocker, located in each pocket, pivots about the pivotaxis toward and away from the cam surfaces. Each rocker has a center ofmass, located relative to the pivot axis when the rocker is retractedinto the pocket away from the cam surfaces, such that an acute angleformed between a first line that extends radially from the central axisthrough the pivot axis and a second line that passes through the centerof mass and the pivot axis is equal to or less than twenty degrees.

Unique fluid passages, partially formed by arcuate spline surfaces, andchannels are provided to carry lubricant to critical surfaces of therockers and notches. Each pocket is closed at one axial end to providestructural continuity, stiffness and strength to carry forces resultingfrom engagement of the rockers with the notches when the clutch isengaged. A spline tooth crest is located near each pocket and indexedrelative to the pocket to provide additional structural strength andstiffness to carry the engagement loads.

A retainer plate, secured to the rocker plate for rotation as a unit,closes the open axial end of the pockets and open axial end of springrecesses to prevent chafing and wear of the rockers and springs. Therocker plate and cam plate have mutually engaged pilot surfaces, whichguide their relative axial movement during assembly and provide mutualbearing support as they rotate.

Other advantages of this invention will become apparent to those skilledin the art from the following detailed description of the preferredembodiment, when read in light of the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side view of a clutch according to the present inventionshowing rockers located in an inner race and engaged with notches in anouter race;

FIG. 2 is an isometric view of the clutch assembly showing thecomponents mutually spaced axially;

FIG. 3 is an isometric view of the clutch assembly of FIG. 2 partiallyin cross section taken at a diametric plane showing the components inspaced relationship;

FIG. 4 is an isometric view of the clutch assembly of FIG. 2 partiallyin cross section through a diametrical plane showing the componentsassembled;

FIG. 5 is a side view, partial cross section through a diametrical planeshowing the components assembled;

FIG. 6 is side view of a portion of an inner race showing a rocker,pocket, and return spring;

FIG. 7 is side view of a portion of an inner race showing a rocker,pocket, return spring, and a CF vector;

FIG. 8 is a side view of a clutch showing rockers located in an outerrace and engaged with notches in an inner race; and

FIG. 9 is side view of a portion of an outer race showing a rocker,pocket, return spring, and a CF vector;

FIG. 10 is side view of an accordion return spring;

FIG. 11 is side view of a helical return spring;

FIG. 12 is a cross section taken at a diametric plane through a one-wayclutch assembly according to this invention;

FIG. 13 is a front view of a retainer plate;

FIG. 14 is a is a side view of the retainer plate of FIG. 13;

FIG. 15 is a local view of the retainer plate taken in the direction ofarrow 15;

FIG. 16 is a end view of a the rocker plate of FIG. 12 looking towardthe axial end that is opposite the open axial end of the pockets;

FIG. 17 is a end view of a the rocker plate of FIG. 12 looking towardthe open axial end of the pockets;

FIG. 18 is a cross section taken at plane 18-18 of FIG. 17;

FIG. 19 is a cross section taken at plane 19-19 of FIG. 17;

FIG. 20 is a side view of an alternate embodiment of cam plate;

FIG. 21 is a cross section taken through a diametric plane of a camplate and rocker plate positioned for piloted assembly on journalsurfaces;

FIG. 22 is a partial end view of the one-way clutch showing the pocketplate installed in the cam plate;

FIG. 23 is a front view of a rocker;

FIG. 24 is a side view of the rocker of FIG. 23;

FIG. 25 is a partial end view of the one-way clutch showing the rockerplate installed in the cam plate, a rocker located in a pocket, and therocker disengaged from and ratcheting on the cams as they rotatecounterclockwise relative to the rocker plate;

FIG. 26 is a partial end view of the one-way clutch similar to FIG. 25,showing a rocker about to engaging the contact face of a cam;

FIG. 27 is a partial end view of the one-way clutch similar to FIG. 25,showing a rocker engaged with the contact face of a cam;

FIG. 28 illustrates the rocker's center of mass located to assistengagement with the cams;

FIG. 29 illustrates the rocker's center of mass located to opposeengagement with the cams;

FIG. 30 is a schematic diagram illustrating the line of action of aforce transmitted between a cam and a rocker pocket when the clutch isengaged;

FIG. 31 is a schematic diagram illustrating the angle of attack betweenthe line of action of FIG. 30 and a line perpendicular to a radial linethrough the pivot axis;

FIG. 32 is a partial end view of the one-way clutch showing the rockerplate installed in the cam plate and a the rocker disengaged from andratcheting on the cams as they rotate counterclockwise relative to therocker plate; and

FIG. 33 is a perspective view of a one-way clutch installed in anassembly showing journal surfaces and body surfaces on the inner ringand outer ring.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring now to the drawings, there is illustrated in FIG. 1 a one-wayclutch assembly 20 in accordance with the present invention. The clutchassembly 20 includes an inner race or rocker plate 22, an outer race orcam plate 24, and a plurality of rockers 26, each rocker being locatedin a pocket 28 formed in the inner race 22 and angularly spaced mutuallyabout a central axis 30. The inner periphery of the outer race 24 isformed with a plurality of cams or notches 32 angularly spaced mutuallyabout axis 30. There are twelve rockers 26 and pockets 28 and thirty-sixnotches 32 in the clutch illustrated in FIG. 1.

When the inner race 22 rotates clockwise faster than the outer race 24,each rocker 26 pivots counterclockwise in its pocket 28 away fromengagement with the notches 32 due to contact of the rockers with theinner radial surface of the outer race. This allows the inner race 22 torotate freely clockwise about axis 30 relative to the outer race 24.When the inner race 22 attempts to rotate counterclockwise relative tothe outer race 24, the inner race and outer race are engaged ordriveably connected mutually by engagement of the rockers 26 with thenotches 32.

When the clutch 20 is engaged, each engaged rocker 26 transmits a forceF between the inner and outer races 22, 24 due to its contact with theinner surface 34 of the pocket and with the radially directed surface 36of the engaged notch 32.

A recess 40, located at each pocket 28, contains a spring, such as ahelical coiled compression spring 42 or an accordion compression spring44, for urging each rocker to pivot in its pocket toward engagement withthe notches.

FIG. 2-5 show a clutch having a rocker plate 22 formed with angularlyspaced pockets 28 and spring recesses 40, each pocket containing arocker 26 that pivots in a respective pocket alternately to engage andto disengage the notches 32 formed on the radially inner surface of thecam plate 24. A bushing 46 of powered metal fits within the cam plate24.

As seen best in FIG. 5, when clutch 20 is assembled, an axial surface ofbushing 46 contacts an inner axial surface 48 of a flange 50. Surface 48is formed with radially directed grooves 52, which carry fluidlubricant, preferably transmission oil, radially outward a radial innersurface of the bushing 46. Oil enters the radial grooves 52 throughholes 49 formed through a drive system component 72, which is connectedto the clutch 20. The oil travels axially leftward across the innerradial surface 51 on the bushing 46, to a radial space 53, which directsthe oil radially outward to surface 55, across the width of the rockerplate 22 and across the surface of the rockers 26. Bushing 46 pilots theinner and outer races 22, 24 and eliminates need to machine along thenotches or cams 32 of the outer race or the radial outer surface area 66of the rocker plate 22. Lubricating oil is precisely directed radiallyalong grooves 52 to the bushing 46, then axially between surfaces 68 onthe rocker plate 22 and the inside diameter 51 of the bushing to therockers 26. The lubricant flows along this path due to a centrifugalpressure head developed as the clutch rotates about axis 30.

The radial outer surface of the cam plate 24 is formed with splines 54,by which the cam plate is driveably connected to a drive system.Similarly, the radially inner surface of the rocker plate 24 is formedwith splines 56, by which the rocker plate is driveably connect to acomponent of the drive system.

An axial surface 58 of rocker plate 22 contacts a retainer ring 60,which closes the axial end of each pocket 28 and is retained in positionby a snap ring 62, which engages a recess 64 formed on the cam plate 24.

FIGS. 3 and 4 show the components of the clutch 20 located immediatelyadjacent their assembled positions and in the assembled positions,respectively. The clutch 20 is assembled with the cam plate 24 driveablyconnected by splines 70 to a drum 72 of a vehicle drive system.

Referring now to FIG. 6, a preferred embodiment of a rocker 26 mayinclude several surfaces 80, 82, 84, 86, 88, and a defined pivot center90. Surfaces 80 and 82 are both circular cylindrical surfaces whose arcsare concentric with the pivot center 90. Surfaces 80, 82 guide rotationor pivoting of the rocker 26 and limit that pivoting to one degree offreedom. The arcs of both surfaces 80, 82 must be sufficient such thatthe neck or strut portion 92 of the rocker is narrower than thecounterweight portion 94 in order to restrain the rocker in the radialdirection from center 90. Surface 80 is a guiding surface. When force Fis applied while the clutch is driving and the rockers 26 are engagedwith the notches 32, preferably no reaction force is developed onsurface 80. Surface 82 is a surface on which the reaction to force F isdeveloped when clutch 20 is transmitting torque between the outer raceand inner race 22 through the rocker 26. Because the center of surface82 is located at the pivot center 90, the reaction to force F isdistributed along surface 82 is centered at pivot center 90, andproduces no torque tending to pivot the rocker 26 about the pivotcenter.

Surface 84 limits clockwise pivoting of the rocker 26 and assistsassembly of the race 22 or 24 that contains the pockets 28, rockers 26and springs 42, 44. That race is prepared for installation by insertinga rocker 26 in each pocket and placing a spring 42, 44 in each recess40. The force applied by the spring on its respective rocker rotates therocker to the position shown in FIG. 6 where surface 84 contacts thebase 96 of the pocket 28. The spring force and its reaction force on thebase 96 retain the rocker in the pocket without the presence of theother race or another assembly aid. The race containing the rockers canbe transported readily with the rockers in this retained conditionpreparatory to installing the race subassembly in the clutch assembly20.

By limiting pivotal rotation of the rocker 26 about pivot center 90, acounter-rotation reaction force on the strut is generated at surface 84when the clutch is driving or engaged. When clutch 20 is driving, forceF, applied to rocker surface 86, produces a clockwise torque on therocker about the pivot center 90. Torque about center 90 produced byforce F is reacted by a force P1 where rocker surface 84 contacts pocketsurface 96. Without surface 84, the full reaction torque would bereacted elsewhere. For example, if the full torsion reaction to force Fwere applied to rocker surface 88, a large hoop stress would begenerated on the race contacted by surface 88 tending to shear the wallof that race due to a high angle of incidence of the reaction force. Ifthe torsion reaction to force F were applied to surface 82, it would beapplied at the extremity of the inner race at its weakest point.Preferably, the torsion reaction to force F is located normal to thepocket base 96 at rocker surface 84, and on surface 82 where friction isdeveloped due to contact with the pocket.

Surface 86 is the surface on which force F is applied when the clutch 20is driving and the rockers 26 are engaged with the radial surfaces 36 ofthe notches 32. Surface 86 performs this function by creating amechanical interference when the rocker is pivoted to the engagedposition.

Surface 88, located at the contour of the strut portion 92 of the rocker26, contacts the crest 98 of the radial surfaces 36 of the notches 32 toensure no interference when the clutch 20 is overrunning and the rockers26 are disengaged from the notches 32. Surface 88 is curved tofacilitate formation of a film of lubricant while the clutch isoverrunning. Surface 88 is curved also to minimize impact with thecrests 98 while the clutch overruns by providing transitional positionsthat minimize the rate of rotation of the rocker into the pocketrelative to the rate of rotation of the outer race. This minimizesangular acceleration on the rocker as the clutch overruns.

The center of mass 100 of the rocker 26 can be located in relation tothe pivot center 90 such that centrifugal force tends either to engageor to disengage the rocker, whether the rocker is located on the outerrace or the inner race.

When viewed as in FIG. 7, the center of mass 100 is located rightwardfrom a line connecting the axis 30 and the pivot center 90, and therocker is carried in a pocket located on an inner race 22. As the clutchassembly 20 rotates about axis 30, centrifugal force on the rocker isdirected radially outward along a line 102 that passes through axis 30and the center of mass 100, causing the rocker 26 to pivotcounterclockwise about the pivot center 90. This counterclockwisepivoting of the rocker opposes the force of the spring 42, 44 and tendsto pivot rocker surface 86 away from contact with pocket surface 36 onthe inner race 24. This counterclockwise pivoting of the rocker tends tomove the rocker to a disengaged position, and allows the inner race 22to overrun and the clutch 20 to disengage. The magnitude of the momentabout pivot center 100 tending to compress spring 42 and to pivot therocker 26 to the disengaged position varies with the speed of rotationof the inner race and the distance of the center of mass 100 from thepivot center 90.

Alternatively the center of mass may be located leftward from a lineconnecting the axis 30 and the pivot center 90, when the rocker iscarried in a pocket located on an inner race 22. In that case, as theclutch assembly 20 rotates about axis 30, centrifugal force on therocker causes the rocker 26 to pivot clockwise about the pivot center90. This clockwise pivoting of the rocker adds to the effect of theforce of spring 42, tends to move surface 86 of the rocker towardcontact with radial surface 36 on the outer race 24, i.e., to pivot therocker 26 to an engaged position, and causes the clutch to engage.

FIG. 8 illustrates an embodiment of a clutch assembly 120, in accordancewith the present invention. The clutch assembly 120 includes an innerrace or rocker plate 122, an outer race or cam plate 124, and aplurality of rockers 126, each rocker being located in a pocket 128formed in the outer race 124 and angularly spaced mutually about acentral axis 130. The outer periphery of the inner race 122 is formedwith a plurality of cams or notches 132, angularly spaced mutually aboutaxis 30. There are nine rockers 126 and pockets 128 and thirty-sixnotches 132 in the clutch illustrated in FIG. 1.

When the outer race 124 rotates clockwise faster than the inner race122, each rocker 126 pivots clockwise in its pocket 128 away fromengagement with the notches 132 due to contact of the rockers with theouter radial surface of the inner race. This allows the outer race 124freely to rotate clockwise about axis 130 relative to the inner race122. When the outer race 124 attempts to rotate counterclockwiserelative to the inner race 122, the inner race and outer race areengaged or driveably connected mutually by engagement of the rockers 126with the notches 132.

When the clutch 120 is engaged, one or more engaged rockers 126 transmita force between the inner race 122 and outer race 124 due to therocker's contact with the inner surface 134 of the pocket 126 and withthe radially directed surface 136 of the engaged notch 132.

A recess 140, located at each pocket 28, contains a spring, such as ahelical coiled compression spring 142 or an accordion compression spring144, for urging each rocker to pivot in its pocket toward engagementwith the notches.

When the clutch assembly 120 is viewed as in FIG. 9, the center of mass150 of each rocker 126 is located rightward from a line connecting theaxis 130 and the pivot center 152. As the outer race 124 rotates aboutaxis 130, centrifugal force on the rocker is directed radially outwardalong a line 154 that passes through axis 130 and the center of mass150, causing the rocker 126 to pivot counterclockwise about the pivotcenter 152. This counterclockwise pivoting of the rocker cooperates withthe force of the spring 42, 44, tends to pivot the rocker to an engagedposition with surface 136, and engages the clutch.

Alternatively, in the clutch assembly 120, the center of mass 150 ofeach rocker 126 may be located leftward from a line connecting the axis130 and the pivot center 152. In that case, as the outer race 124rotates about axis 30, centrifugal force on the rocker causes the rocker126 to pivot clockwise about the pivot center 152. This clockwisepivoting of the rockers opposes the effect of the spring force and tendsto pivot rotate surface 86 of the rocker away from contact with radialsurface 136 on the inner race 122. This action tends to move the rockerto a disengaged position, and allows the clutch to overrun and todisengage.

Referring now to FIG. 12, an alternate clutch assembly, similar to thatof FIGS. 1 and 8, includes a cam plate 160 formed with cam surfaces ornotches 162, a radial flange 164 located at an axial end of the camplate, a cylindrical interior journal surface 180, and a recess 166formed in the journal surface 180 and located axially opposite flange164.

A rocker plate 168 is formed with multiple pockets 170, angularly spacedat equal intervals about a central longitudinal axis 172, each pocketcontaining a rocker 174. Each pocket 170 is blind, i.e., closed at oneaxial end by the surface 176 of a bulkhead. Each pocket has an axialopen end located at the opposite axial end from surface 176. Thebulkhead has an exterior surface 196 that faces axially outward from issurface 176. Each pocket 170 has an aperture located at its radialperiphery and facing the cam surfaces 162, as FIGS. 1 and 8 illustratefor clutches 20 and 120. A portion of each rocker 174 pivots into theaperture of the respective pocket as the rocker pivots to toward the camsurfaces on cam plate 160. When the clutch overruns, each rockerratchets on the cam surfaces as they contact and rotate past therockers. The open end 177 of each pocket 170 and an axial end of eachspring recesses 40 are covered by a retainer plate 178. Wear resultingfrom contact of the rocker and spring on a surface adjacent the end 177is prevented by the retainer plate 178.

In the embodiment of FIG. 12, the cam plate 160 is formed with aninternal, axially directed cylindrical journal surface 180, and therocker plate 168 is formed with an external, axially directedcylindrical journal surface 182. The cam plate and rocker plate arepiloted on the journal surfaces 180, 182 for axial movement to theassembled position shown in FIG. 12. Upon installation, surfaces 180,182 are mutually engaged and provide bearing support for relativerotation of the cam plate and rocker plate. A retainer ring 184 seats inthe recess 166 to secure the rocker plate 168 against axial movementrelative to the cam plate 160 after their assembly and during operation.

Turning now to FIGS. 13-15, the retainer plate 178 is a substantiallyplanar circular ring 190, whose axial inner surface is located adjacentthe open axial end 177 of the pockets 170. Angularly spaced tabs 192extend axially from the surface of ring 190 toward the rocker plate 168,to which the retainer plate 178 is secured for rotation with the rockerplate. An inner periphery 194 of the retainer plate is formed with acontour similar to a spline having alternating crests and valleysangularly spaced about axis 172. FIG. 15 shows a typical axiallydirected tab 192 that extends from the plane of surface 190 of theretainer plate 178 and the adjacent relief recesses 191, whichfacilitate bending the tabs into position.

In an alternative form, the retainer plate 178 may be a disc that iswelded, preferably by capacitive discharge welding, to the rocker plate168. In this case, the angularly spaced tabs 192 that extend axiallyfrom the surface of ring 190 toward the rocker plate 168 are eliminatedand the tab recess 220, shown in FIG. 17, are eliminated from the rockerplate.

Referring to FIG. 16, the face 196 of the rocker plate 168 that isaxially opposite the open axial end 177 of the pockets 170 is formed atits radial inner surface with an interior spline, which extends axiallyacross the rocker plate. The spline contour includes alternating crests202 and valleys 204 angularly spaced about axis 172 and connected bytooth faces 203. The interior spline, which has a major diameter 206, isdriveably engaged by an external spline on a component connected by thesplines. The spline valleys 204 each have an arcuate base that creates aspace for a fluid passage 208 between the major diameter 206 and thebase of the valley 204.

FIG. 18 shows that the passages 208 are directed axially across therocker plate from surface 196 toward the open axial end 177 of eachpocket 170 and radially outward from axis 172. Fluid lubricant, carriedin the fluid passages to the retainer plate 178, flows between therocker plate surface 210 and the axially inner surface 212 of theretainer plate 178 into the pocket 170 and radially outward against thenotches 162 of the cam plate 160. In this way, the rocker, pocket andnotches are continually lubricated.

Referring now to FIGS. 17 and 19, the surface 210 of rocker plate 168that which is axially opposite surface 196 is formed with angularlyspaced radial channels 216, each channel being located betweensuccessive, adjacent pockets 170. Each channel 216 extends from thespline valleys 204, radially across surface 210 and is covered by theretainer plate 178. Fluid lubricant exiting channels 216 is thrownradially outward against the surfaces of the notches 162 on the camplate 160

The axial surface 210 is also formed with angularly spaced tab recesses220, which are located and sized to receive the tabs 192 of the retainerplate 178. When the tabs 192 are engaged with the recesses 220, retainerplate 178 is located adjacent the axial surface 210 of the rocker plate168, and the retainer plate is secured to the rocker plate so that theyrotate as a unit.

When the clutch becomes engaged, at least one rocker in a pocket 170 ofthe rocker plate 168 becomes engaged with a notch 162 on the cam plate160, and a force F is applied to the rocker, as shown in FIG. 1. Theexternal force applied to the engaged rocker is transmitted to a corner222 of the respective pocket 170, where the applied force F is reactedon rocker plate 168.

According to another aspect of this invention, the internal splines atthe inner radial periphery of rocker plate 168 are angularly positionedabout axis 172 and indexed relative to the corner 222 of each pocket 170such that a spline crest 202 is located at an extension of the line ofaction of the force represented by vector F. The line of action of forceF extends from the mid-point on surface 86 of a rocker 26 that isengaged with a cam 36 to the opposite corner of the pocket where theengagement force applied by the cam is reacted on the pocket wall. AsFIG. 17 shows, the preferred location of the spline crest 202 is suchthat the line of action of force F passes through the crest at point224, substantial midway between the angular extremities of the crest.This location of the crest relative to the

To ensure that the spline crest is so positioned and indexed to providethe desired structural advantage produced by its correct location, thespline crest 202 is located radially below and angularly offset from thenearest pocket 170 and its corner 222, and the spline valley 204 that isnearest each pocket is radially below and angularly aligned with thepocket.

Referring now to FIGS. 20 and 21, a one-way clutch assembly similar tothat of FIG. 12 includes a circular cam plate 300 formed with cams 302,spaced angularly about central longitudinal axis 304; a radial flange303, located at an axial end of the cam plate; and a recess 305, locatedat the opposite axial end of the cam plate. Each cam 302 includes acontact face 308, a convex cam surface 306 directly radially outward andangularly about axis 304, and an undercut 310 or fillet radius, whichforms a transition between contact face 308 and cam surface 306.Undercut 310 provides relief against a stress concentration that wouldotherwise be present if the stop surface 308 intersected cam surface 306at and acute angle. There are approximately 37 cams formed on the innerperiphery of the cam plate 300. Surfaces 306, 308 and 310 extend to theinner surface 315 of the radial flange 303 and axially parallel tocentral axis 304.

A journal surface 312, for supporting a rocker plate formed with amating journal surface 182, is interrupted by recess 305, which containsa snap ring 184 fitted resiliently in the recess 305, as is shown inFIG. 12. The cam plate 300 is formed with an internal, axially directedcylindrical journal surface 312, and the rocker plate 320 is formed withan external, axially directed cylindrical journal surface 182. The camplate and rocker plate are piloted on the journal surfaces 312, 182 foraxial movement to the assembled position. Upon installation, surfaces312, 182 are mutually engaged and provide bearing support for relativerotation of the cam plate and rocker plate. A retainer ring 184 seats inthe recess 305 to secure the rocker plate 320 against axial movementrelative to the cam plate 160 after their assembly and during operation.

As described with reference to the clutch illustrated in FIGS. 12-19,lubricant flows radially outward on the inner face 315 of flange 303after exiting the fluid channels 204, 208. The lubricant flows againstthe concave cam surface 306, contacts surface 308, and tends toaccumulate in each undercut 310.

The contact surface 308 of each cam 302 is substantially parallel to andspaced from a respective plane 314, which extends radially outward fromcentral axis 304 and is located angularly about axis 314 at each camlocation. The cam surface 306 is formed from several circular arcs,which transition gradually, radially outward toward undercut 310 andangularly about axis 304.

FIG. 17 shows a rocker plate 168 formed with seven pockets 170, whichare angularly spaced about a central axis 172. FIG. 22 illustrates aportion of an alternate rocker plate 320 fitted within the inner radialperiphery of cam plate 300. Rocker plate 320 also includes seven pockets322, angularly spaced at equal intervals about central axis 304. Thebase of each pocket 320 is formed with a concave cylindrical surface324, a second concave cylindrical surface 326, and a planer surface 328tangential to surfaces 324, 326. The radially outer end of spring recess327 transitions to a planer surface 330 using a fillet radius 322. Atransition from planer surface 330 and cylindrical surface 324 is madeusing a rocker retention projection 332, whose center is locatedexternally from the pocket 322. The center of cylindrical surface 324 islocated on a pivot axis 334, which passes axially through the thicknessof rocker plate 320 and is substantially parallel to central axis 304.

Each pocket 322 is blind, i.e., closed at one axial end by surface 176and is open at the opposite axial end 177. Each pocket 322 has anaperture or opening 323 at its radial outer periphery, through whichopening a portion of the respective rocker 340 passes as it pivots toengage and disengage the cams 310, which face the pockets 322. However,the rocker 340 cannot be removed from its pocket through the aperture323 because the installed rocker is retained or trapped there by theundercut or fillet 332. FIG. 25 shows the rocker 340 retained in thepocket 322 due to contact between rocker retention projection 332 andthe undercut 354, and the rocker contacting surfaces 324 and 326.Therefore, each rocker 340 is inserted or installed in the respectivepocket 322 and is removed from the pocket using access provided at theopen end 177 at axial end surface 210.

A rocker 340 of the type that is installed in each pocket 322 isillustrated in FIGS. 23 and 24. The rocker includes a convex cylindricalsurface 342, which is complementary to pocket surface 324, a secondconvex cylindrical surface 346, which is complementary to pocket surface326, and a concave or recessed surface 352 that blends tangentially withsurfaces 342, 346. Pocket surface 324 has a center at 344, which uponinstallation of the rocker 340 in the pocket 322 is substantiallyparallel to, or coincident with the pivot axis 334. Recess 352 preventsthe rocker from contacting planer surface 328 of the pocket 322.

The rocker is formed with a fillet radius 354, whose center is at 356.The fillet radius 354 and its adjacent surfaces 358, 360 form anundercut 354 that retains the rocker 340 in the pocket 322 and preventsit from exiting radially from the pocket 322 through the aperture 323.The rocker extends from the undercut 356 to an engagement face 362,which engages contact face 308 of the cam 302 when the clutch isengaged. The radial outer surface 364 of the rocker 340 is formed withvarious circular arcs, one arc having a center at 366, other arcscompleting a smooth transition to rocker surface 346.

The contour of surface 364 is formed such that a space located between aportion of its length and a portion of the contour of cam surface 306,when the clutch is overrunning and the rocker is ratcheting on the camplate, contains hydraulic fluid, preferably lubricant or automatictransmission fluid that has been supplied to the cam surface 306, asdescribed with reference to FIGS. 16-19. FIGS. 25 and 26 show hydraulicfluid 376 in the space between the contours of the cam surface 302 andthe rocker surface 364.

FIG. 24 shows the approximate location of the rocker's center of mass350, located mid-way between the end faces and closer to surfaces 342,346 than to the engagement surface 362.

FIG. 25 shows the rocker 340 disengaged from the cam ring 300 andratcheting on the cams 302 as they rotate counterclockwise relative tothe rocker plate 320. The rocker surface 342 is engaged with pocketsurface 324 causing the rocker 340 to engage the pocket 322 in a socketjoint. A spring 370, located in spring recess 327, urges the rocker 340to pivot about pivot axis 334 causing rocker surface 364 to pivot aboutpivot axis 334 toward engagement and into contact with surface 306 ofeach cam as it passes the rocker 340. The rocker is restrained fromexiting the pocket 322 due to engagement of its undercut 354 with thepocket's undercut 322. A bead of hydraulic lubricant 376 present on camsurface 306 is located between cam surface 306 and the radial outersurface 364 of the rocker 340, thereby dampening or cushioning contactbetween the rocker and cam as the clutch overruns.

The rockers 340 continue to ratchet on the cams 302 while the cam ring300 rotates counterclockwise relative to the rocker ring 320. As FIG. 26illustrates, when the corner 372 of each rocker clears the corner 374 ofthe cam's contact surface 308, the rocker springs radially outward intocontact with the cam surface 306. FIG. 26 shows the rocker 340 havingcleared corner 374 of the contact surface 308 but before engagementsurface 362 and contact face 308 become engaged. Hydraulic lubricant 376present on cam surface 306 becomes located between cam surface 306 andthe radial outer surface 364 of the rocker 340, thereby dampening orcushioning contact between the rocker and the cam. As the rockerratchets on the cams 302, lubricant 376 located on cam surface 306 andundercut surface 310 is compressed by the ratcheting motion of therocker 340 and is pumped axially away from radial flange 303 of the camplate 300 and the cam surfaces 306, 308 310 to the journal surface 312.In the example described here, this pumping action, which occurs wheneach of thirty-seven cams 302 ratchet over seven rockers 340 perrevolution of the cam plate 300 relative to the rocker plate 320,provides continuous lubricant flow to the journal surface 312 of the camplate and the mating journal surface of the rocker plate.

The clutch overruns while cam plate 300 rotates faster than, and in thesame direction as the rocker plate 320. When the speed of the rockerplate 320 equals or exceeds that of cam plate 300 or the cam platerotates in the opposite direction from the rocker plate, the clutchengages. Engagement occurs when the corner 372 of a rocker 340 clearsthe corner 374 of the cam's contact surface 308, thereby allowing therocker's engagement surface 362 to engage the cam's contact surface 308.As this engagement occurs, the rocker 340 pivots clockwise about pivotaxis 334 from the position of FIGS. 25 and 26, and rocker surface 346 isforced against pocket surface 326, as shown in FIG. 27. When the clutchis engaged, force F, which is transmitted between the rocker plate 320and cam plate 300 as described with reference to FIG. 17, forces rockersurface 346 against pocket surface 32 and opens a clearance spacebetween pocket surface 324 and the adjacent rocker surface 342.

In FIG. 28, the direction of a radial line 380, drawn from the centralaxis 304 through the pivot axis 334, represents the radial direction ofcentrifugal force acting on the components of the clutch. Line 382 is astraight line containing points representing the pivot axis 334 andcenter of mass 350 of the rocker 340. When the rocker plate 320 rotatesabout axis 304, the centrifugal force of the rocker, represented byvector J, is directed radially from axis 304 through the rocker's centerof mass 350. The rocker is shown in FIG. 28 fully retracted within thepocket, i.e., rotated in the pocket counterclockwise about pivot axis334 until contact between the rocker and the rocker plate preventsfurther rotation. With the rocker in that position, its center of mass350 is located relative to the pivot axis 334 such that centrifugalforce J applied to the rocker 340 causes the rocker to pivot clockwiseabout pivot axis 334, thereby assisting the force of spring 370 inpivoting the rocker toward engagement with the cams 302. However, withthe clutch operating in its normal range of rotational speed, themagnitude of force J far exceeds the magnitude of the force produced byspring 370.

Centrifugal force J pivots each rocker 340 about axis 334 such that therocker's outer surface 364 extends through the aperture 323 on thesurface of the cam plate 300 to the position shown in FIG. 25, wheretransmission fluid 376, or another hydraulic fluid, attenuates orcushions repetitive contact between the cam surfaces 306 and therocker's outer surface 364 as the clutch overruns.

Because the spring force is small relative to the magnitude of therocker's centrifugal force, the magnitude, direction and location offorce J are the primary variables that establish a preferred angularrange of the rocker about pivot axis 334 as the clutch overruns. FIG. 25shows the rocker 340 in that preferred range . . . It has beendetermined that when the rocker 340 is fully retracted within the pocketa preferred range of the acute angle 384 formed by the intersection ofradial line 380 and line 382 is in the range between zero degrees and 20degrees.

The rocker 340′ is shown in FIG. 29 fully retracted within the pocket,i.e., rotated in the pocket counterclockwise about pivot axis 334 untilcontact between the rocker and the rocker plate prevents furtherrotation. The rocker's center of mass 350′ is located relative to thepivot axis 334 such that the rocker's centrifugal force K, which isdirected radially from the mass center 350′, causes the rocker 340′ topivot counterclockwise about pivot axis 334 away from the cams 302 inopposition to the force of spring 370. However, the force of spring 370,which opposes counterclockwise pivoting of the rocker, at low rotationalspeed, is high relative to the centrifugal force on the rocker. Radialline 380 extends from central axis 304 through the pivot axis 334, and aline 386 extends from the pivot axis to the rocker's center of mass350′. In the case when centrifugal force operates to disengage theclutch and the rocker 340 is fully retracted within the pocket, apreferred range of the acute angle 388 formed by the intersection ofradial line 380 and line 386 is in the range between zero degrees and 20degrees.

When a cam 310 is engaged by a rocker 340, the force F applied to therocker by the cam that is engaged by the rocker and its reaction R onthe pocket where the rocker is located can be represented by a straightline 390. Line 390 connects the mid-point 392 of the area of contactbetween the rocker and the contact face 308 of the engaged cam, and themid-point 394 of the area of the second concave cylindrical surface 326contacted by the convex rocker surface 346. FIGS. 30 and 31 show thesepoints, lines and surfaces.

The tangential component of force F, which is perpendicular to radialline 380, induces a torsion moment in the rocker plate about axis 304tending to rotate the rocker plate 320 with the cam plate 300 as a unitabout axis 304. The loading applied to the pocket at the reaction R isdistributed angularly about the center of cylindrical surface 326 andaxially across the depth of the pocket. The distributed loading has apeak magnitude at line 390 and a decreasing magnitude as distance fromline 390 increases. The peak magnitude of the distributed loading isalong line 390 and has no radial component about the center of pocketsurface 326. However, the radial components of the distributed loadinginduce tensile stress in the cam plate.

To avoid a tension failure of the cam plate due to this loading, anaxial end 176 of each pocket is closed by a bulkhead face 196 locatedaxially opposite the open axial end 177, thereby providing radialtension continuity across the pocket opening. The stiffness of thebulkhead further causes the distributed loading on the pocket caused byForce F to be concentrated at the axial end of the pocket that isclosest to the bulkhead.

Referring now to FIG. 31, when a cam 310 is engaged by a rocker 340, anangle 398 is formed between the line of action 390 and a line 400 thatis perpendicular to the radial line 380 that extends from the rockeraxis 304 to the pivot axis 334. When angle 398 is large, the radialcomponent of force F, parallel to line 380, is relatively large, and thetangential component, parallel to line 400, is small. Therefore, whenangle 398 is large, force F has less of a tendency to rotate rockerplate 320 about the central axis 304 and more of tendency to force therocker plate radially toward axis 304. But when angle 398 is smaller,the radial component of force F parallel to line 380 and tending torotate the rocker plate about axis 304, is relatively large, and itstangential component is small. It has been determined that a preferredrange of the angle 398 is between zero degrees and 45 degrees. In thatrange, the magnitude of material stress, induced in the rocker plate byradial directed load, are lower than the strength capacity of the rockerplate material.

Referring to FIG. 32 in which a rocker plate 320 is shown installed in acam plate 300, the rocker 340 located in pocket 322 is ratcheting on thecams 310 as the cam plate rotates counterclockwise relative to therocker plate. The cam plate and rocker plate are located such that therocker's outer surface 364 is in contact with cam surface 306 at theline 410, whose trace appears in the FIG. 32 as a point, on whichsurfaces 364 and 306 first make contact as the cams movecounterclockwise across the rocker. Line 308 is a straight radial lineextending from the central axis 304 through the pivot center 334. Line412 is a straight line connecting pivot center 334 and the center of theline contact 410 on the rocker surface 364. Angle 414 is formed by theintersection of lines 308 and 412.

In order to minimize the magnitude of the radial component of the forceproduced by contact between rocker 364 and cam surface 306, preferablyfirst contact 410 between the rocker and cam occurs on the trailing sideof radial line 308, i.e., after the cam rotates past line 308.Preferably, the angular offset of the first contact from line 308 issufficient to minimize the magnitude of the radial component of thecontact force. It has been determined that angle 414 is preferablygreater than ten degrees and should be in the range 10-45 degrees.

FIGS. 21 and 33 illustrate a technique for piloting the cam plate 300and rocker plate 320 to their assembled positions. In FIG. 21, the camplate 300 is formed with an internal, axially directed cylindrical pilotor journal surface 312. Rocker plate 320 is formed with an external,axially directed cylindrical pilot or journal surface 318, on which thecam plate's surface 312 is piloted for axial movement to the assembledposition. Upon installation, surfaces 312, 318 are mutually engaged andprovide bearing support for relative rotation of the cam plate 300 androcker plate 320. A retainer ring seats in the recess 305 to secure therocker plate 320 against axial movement relative to the cam plate 300after their assembly and during operation.

FIG. 33 shows the rocker one-way clutch having it cam plate 300encircling the rocker plate 320. The hub 420, located in thetransmission on a nonrotating support, is the primary reference locatorof the assembly. Although there is clearance between the hub 420 andinner plate 320 to allow their assembly, they could be a pressedtogether or formed of a single piece. The support (not shown) isconnected to a transmission case and does not rotate. The hub 420 isconnected to other transmission components, which apply energy to thehub causing it to rotate.

The inner race 320, which is illustrated in FIG. 33 as a rocker platebut could be a cam plate, is formed with a stepped cross section, whoselarger diameter is machined to create the diameter of journal surface318. The hub 420 locates the radial position of rocker plate 320. Thesplines 422 between the hub 420 and rocker plate 320 force those twocomponents to maintain zero relative speed and to transfer torquebetween them. Components attached to the hub locate the rocker plate 320axially.

In one example, the minimum and maximum dimensions of the diameter ofthe rocker plate journal surface 318 are 5.0205 and 5.0235,respectively. The minimum and maximum dimensions of the diameter of therocker plate body surface 424 are 4.8450 and 4.8550, respectively.

The minimum and maximum dimensions of the diameter of the cam platejournal surface 312 are 5.0265 and 5.0305, respectively. The minimum andmaximum dimensions of the diameter of the cam plate body surface 302 are4.8725 and 4.8775, respectively.

From these dimensions it can be seen that the maximum clearance betweenthe cam plate and rocker plate race occurs between the body surfacediameters 424, 302, where the maximum and minimum clearance is 0.0325and 0.0175, respectively. The minimum clearance between the two platesoccurs at the journal surfaces 312, 318, where the maximum and minimumclearance is 0.0100 and 0.0030, respectively.

A reason that the clearance between journal surfaces 312, 318 is lessthan the clearance between the body surfaces 424, 302 is to ensure thatthe cam plate body surface diameter 424 does not contact the rockerplate body diameter 302. The adjacent body surfaces are cylindrical,intermittent surfaces, interrupted by the pocket apertures 323, whichcould cause instantaneous lockup of the two plates during high speedoverrun, were it not for the dimensional clearance precautions beingdiscussed here. The journal surface diameters also maintain the relativeposition of the cam or outer plate 300 relative to the rocker or innerplate 320 during lockup. It is possible that only one rocker 340 mayengage a cam during lockup. When this occurs, the outer plate 300 tendsto rotate about the engaged rocker at the area of contact engagement.The small clearance at the journal interface 312-318 allows the outerplate 300 to rotate only a small distance before mutual contact of thejournal surfaces 312, 318 occurs. The tight clearance at the journalsurfaces restricts radial play of the outer plate 300 with respect toclearance to of the inner plate 320 during all modes ofoperation—overrun, transition, and lockup.

Journal surfaces 312 and journal surface 318 are cylindrical surfaces.Journal surface 318 is piloted on surface 312, thereby reducing thepotential for the two surfaces to weld together. The sharp edges of theundercuts 310 on the outer plate 300 tend to disrupt the oil film thatforms at the interface. If both surfaces were intermittent the innerplate 320 and outer plate 300 would contact at these high stress pointsand could weld or stick. The continuous journal surface distributes theloading, which reduces the potential for welding.

Alternatively, piloting the inner and outer plates 300, 320 can beperformed using a third component, such as hub 420. In this case, arelatively tight dimensional tolerance is established between thediameter of surface 416 of the outer plate 300 and the diameter ofsurface 430 of the hub 300, which becomes located close to surface 416by extending flange 303 radially toward hub surface 430. The magnitudeof the clearance between the diameters of the flange surface 416 and hubsurface 430 is similar to the maximum and minimum clearance describedabove between the inner and outer plates at journal surfaces 312, 318.

A second relatively tight dimensional tolerance is established betweenthe diameter of surface 432 of the inner plate 320 and the diameter ofsurface 430 of the hub 300, similarly to the maximum and minimumclearance described above between the inner and outer plates at surfaces312, 318. These two clearances, at the 430-432 interface and 416-430interface, produce a predetermined clearance at the journal interface312-318.

The journal surface interface 312-318 is axially spaced from the cams302 and rockers 340. This allows the number of cams to be maximized,thereby reducing backlash, which can produce an objectionable noise,such as a clunking sound. Other overrunning clutches in the prior artattempt to use the body diameters for piloting the inner and outerplates. These clutches require a significant portion of the outer platebody surface area to be smooth and uninterrupted for piloting, thusreducing the size of the remaining area, permitting fewer cams to occupythe residual area, and increasing the risk of backlash.

In accordance with the provisions of the patent statutes, the principleand mode of operation of this invention have been explained andillustrated in its preferred embodiment. However, it must be understoodthat this invention may be practiced otherwise than as specificallyexplained and illustrated without departing from its spirit or scope.

1. An overrunning one-way clutch comprising: a cam plate formed with camsurfaces angularly spaced about a central axis; a rocker plate includingpockets angularly spaced about the central axis, each pocket including asurface having a pivot axis located within the pocket; a plurality ofrockers, each rocker located in a pocket for pivoting about the pivotaxis toward and away from the cam surfaces, each rocker having a centerof mass, located relative to the pivot axis when the rocker is retractedinto the pocket away from the cam surfaces, such that an acute angleformed between a first line that extends radially from the central axisthrough the pivot axis and a second line that passes through the centerof mass and the pivot axis is equal to or less than twenty degrees; andsprings supported on the rocker plate, each spring urging a rockertoward the cam surfaces.
 2. The clutch of claim 1 wherein said acuteangle is in a range between zero degrees and twenty degrees.
 3. Theclutch of claim 1 wherein the center of mass is located relative to saidpivot axis such that, upon rotation of the rocker plate about thecentral axis, each rocker is biased by centrifugal force toward the camsurfaces.
 4. The clutch of claim 1 wherein the center of mass is locatedrelative to said pivot axis such that, upon rotation of the rocker plateabout the central axis, each rocker is biased by centrifugal force awayfrom the cam surfaces.
 5. An overrunning one-way clutch comprising: arocker plate formed as an radially inner ring including pocketsangularly spaced about a central axis, each pocket including a surfacehaving a pivot axis located within the pocket; a cam plate formed as aradially outer ring encircling the rocker plate, including cam surfacesangularly spaced about the central axis and facing the pockets; and aplurality of rockers, each rocker located in a pocket for pivoting aboutthe pivot axis toward and away from the cam surfaces, each rocker havinga center of mass, located relative to the pivot axis when the rocker isretracted in the pocket away from the cam surfaces, such that an acuteangle formed between a first line that extends radially from the centralaxis through the pivot axis and a second line that passes through thecenter of mass and the pivot axis is equal to or less than twentydegrees.
 6. The clutch of claim 1 wherein said acute angle is in a rangebetween zero degrees and twenty degrees.
 7. The clutch of claim 5further comprising springs supported on the rocker plate, each springurging a rocker toward the cam surfaces.
 8. The clutch of claim 5wherein the center of mass is located relative to said pivot axis suchthat, upon rotation of the rocker plate about the central axis, eachrocker is biased by centrifugal force toward the cam surfaces.
 9. Theclutch of claim 5 wherein the center of mass is located relative to saidpivot axis such that, upon rotation of the rocker plate about thecentral axis, each rocker is biased by centrifugal force away from thecam surfaces.
 10. An overrunning one-way clutch comprising: a cam plateformed as a radially inner ring, including cam surfaces angularly spacedabout a central axis; a rocker plate formed as an radially outer ringencircling the cam plate, including pockets angularly spaced about thecentral axis and facing the cam surfaces, each pocket including asurface having a pivot axis located within the pocket; a plurality ofrockers, each rocker located in a pocket for pivoting about the pivotaxis toward and away from the cam surfaces, each rocker having a centerof mass, located relative to the pivot axis when the rocker is retractedin the pocket away from the cam surfaces, such that an angle formedbetween a first line that extends radially from the central axis throughthe pivot axis and a second line that passes through the center of massand the pivot axis is equal to or less than twenty degrees.
 11. Theclutch of claim 10 further comprising springs supported on the rockerplate, each spring urging a rocker toward the cam surfaces.
 12. Theclutch of claim 10 wherein the center of mass is located relative to thepivot axis such that, upon rotation of the rocker plate about thecentral axis, each rocker is biased by centrifugal force toward the camsurfaces.
 13. The clutch of claim 10 wherein the center of mass islocated relative to the pivot axis such that, upon rotation of therocker plate about the central axis, each rocker is biased bycentrifugal force away from the cam surfaces.
 14. The clutch of claim 10wherein said angle is in a range between zero degrees and twentydegrees.